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TEXT-BOOK OF ENTOMOLOGY 



8. Internal medullary mass. (Opt icon of Hickson.) 



9. Optic ganglia and nerves. 



10. Pedunculated or stalked body. (Mushroom body of Dujardin.) 



11. Bridge of the procerebral lobes. 



12. Central body. 



Optic ganglia. - - Each of the two optic ganglia is formed of a 

 series of three ganglionic masses situated between the compound 

 eyes and the median procerebral mass, i.e. the ganglionic plate 



FIG. 249. Diagram of an insect's brain: cc, central body; eg, ganglionic cells; che, external, 

 chi, internal chiasma ; c<e. <e.sophageal commissure; up, mushroom body; etc, tritocerebral com- 

 missure ; fpr, post-retinal fibres ; goc, ocellar ganglion ; ffoe 1 , nesophageal ganglion, the dotted ring 

 the (esophagus ; gr> 1 , f/c 2 , f/w 3 , 1st, 2d, 3d, unpaired visceral ganglion ; gvl, lateral visceral ganglion ; 

 Id, dorsal lobe of tin- deutocerebrum ; /#, ganglionic plate; /<>, olfactory lobe; Ipc, protocerebral 

 lobe; rue, external, mi. internal medullary mass; nil, olfactory or antenna! nerve; nl, nerve to 

 labruin ; no, ocular nerve ; >it, tegumentary nerve ; <f, cpsophagus ; plji, bridge of the protocerebral 

 lobes; rvd, visceral root arising from the deutocerebrum ; rrt, visceral root arising from the trito- 

 cerebrum ; tr, tritoi-erebrum ; to, optic nerve or tract. After Viallanes. 



(Fig. 249, Ig), the external medullary mass (me. ), and the internal 

 medullary mass (rni). 



The postretinal fibres (fpr) arising from the facets or single eyes of 

 the compound eye (ommatidia) pass into the ganglionic plate (Ig), 

 which is united within by the chiasmatic fibres (die, external chiasma) 

 of the external medullary mass (m.( j ). The last is attached to the 

 internal medullary mass (mi} by fibres (chi), some of which are chias- 

 matic, and others direct. Finally, the internal medullary mass con- 

 nects with the median part of the protocerebrum by direct fibres 

 forming the optic nerve or tract (to). 



Procerebral lobes. - -The median procerebral lobes are fused together 

 on the median line, forming a single central mass. From each side 



